Transistor bridges are commonly used to drive electric loads (including electro-mechanical loads such as electric motors). One simple transistor bridge is a half-bridge, which can be used to drive various types of single-ended loads. So-called H-bridges are usually used to drive loads such as stepper motors. So called three-phase transistor half-bridges can be used to drive a 3-phase electric motor (e.g. a brushless DC motor, BLDC motor). Such three-phase transistor half-bridges are often referred to as three-phase bridges or three-phase inventers and are essentially composed of three transistor half bridges. Transistor bridges are power electronic de-vices which usually are operated by a bridge driver circuit. A bridge driver circuit includes circuitry configured to switch die transistors of the transistor bridge on and off in a defined manner. For example, the bridge driver may be configured to switch die transistors of a three-phase bridge on and off to implement an electronic commutation for a BLDC motor.
In many applications and particularly when driving electric motors it is often desired to detect faulty loads. Therefore, many bridge driver circuits include circuitry for detecting over-currents caused by short-circuits. In this case the transistor bridge needs to be activated so that an over-current can pass through the short-circuited load, before the over-current (and thus the short-circuit) can be detected and a protection mechanism (over-current shut-down) can be triggered. However, such a protection mechanism may be too slow in some application and current spikes may still damage the system (particularly the transistor bridge). Even if potential damage is not an issue, it may be desired to have information about the state of the load before switching on the transistor bridge. Furthermore, an open circuit (open load) detection may be desired in some applications.